The invention concerns a measuring gas pump with a pump housing containing a pump chamber sealed with a working membrane which is connected to a crank mechanism through a connecting rod with a crank mechanism, and in which a heating device is provided in the upper area of the pump housing, as well as with a heating device located in the upper area of the pump housing. In the drive-transmission area between the head of the connecting rod on the membrane side and the crank mechanism, holes are provided for purposes of reducing heat transfer to the crank mechanism by reducing heat conductivity. These holes are spaced in the longitudinal direction of the connecting rod and are offset in peripheral direction.
In U.S. Pat. No. 4,790,730, a measuring gas pump of the type mentioned above, for the delivery of hot measured gasses, is known, in which the working membrane sealing the pump chamber is connected to a crank mechanism by a connecting rod. In the pump previously known from U.S. Pat. No. 4,790,730, a heating device is located in the upper area of the pump housing. With the help of this heating device, the areas which come into contact with the gas to be measured are supposed to be maintained at a pre-determined temperature equivalent to that of the extraction point of the gas to be measured, in order to prevent a drop in temperature of the gas to be measured in the area of the pump chamber and to avoid a condensation of gas components to be analyzed and a falsification of the measurement results.
In the pump of U.S. Pat. No. 4,790,730, holes, spaced in the longitudinal direction of the connecting rod and offset in peripheral direction, are provided for the purpose of reducing heat transfer to the crank mechanism in the drive-transmission area between the head of the connecting rod on the membrane side and the crank mechanism, therefore reducing heat conductivity. At the same time, however, the connecting rod in the area of these holes features a larger connecting rod cross-section, thus reducing the thermal resistance in an undesirable manner.
The object of this invention is to reduce the transfer of heat between the pump head and the crank mechanism, particularly to the bearing of the connecting rod, while largely avoiding the disadvantages described above.
In order to accomplish this task, it is suggested that an enlargement of the surface area be provided in the form of cooling ribs, for purposes of heat dissipation, located in the area of the head of the connecting rod adjacent to the crank mechanism where the rod portion of the connecting rod is connected, and that at least one hole be provided for reducing heat conductivity and/or for heat dissipation to the adjacently located cooling ribs in the area between the cooling ribs and the bearing of the connecting rod.
The combination of these simple-to-institute measures leads to an effective reduction of the temperature of the bearing of the connection rod, resulting in a corresponding extension of service life. In the head of the connecting rod adjacent to the crank mechanism of the invented gas pump, one or several holes are also provided in the area between the cooling ribs and the bearing of the connection rod for reducing heat conductivity and/or for dissipating heat to the adjacently located cooling ribs. On the one hand, this reduces the surface area of the heat conducting cross-section. On the other hand, air circulation and, therefore, heat dissipation can be achieved by means of these holes. In addition, this favors the drawing off of heat to the cooling ribs.
Cooling by means of the cooling ribs is especially effective by means of the crank or eccentric movement, so that practically no elevated temperature load on the bearing of the connection rod and its surrounding area occurs, in spite of higher temperatures in the area of the head of the connecting rod.
The holes, spaced on the side and offset in peripheral direction, minimize the heat conducting cross-section of the connecting rod, but reduce the stability only insignificantly by the longitudinal offset of the holes. The heat still occurring at the end of the connecting rod adjacent to the crank mechanism can then be effectively dissipated into the environment through the increase in surface area provided by the cooling ribs.
The adjacent holes should be diametrically opposed at 90xc2x0 to each other with a medium amount of distance that is no less than the diameter. Through this side offset of the holes in the longitudinal direction of the connecting rod, the holes indeed interlock, the result being an especially good aeration and cooling in this area as well, but the stability of the connecting rod is preserved to the greatest extent possible.
Another advantage is that the connecting rod is made of steel, specifically from stainless steel. Stainless steel has the advantage over the aluminum used most of the time for connecting rods, since it has less heat conductivity but good stability characteristics at the same time.
The described invention is particularly advantageous when used with gas pumps featuring heat insulation that encompasses at least the pump head, so that the heat insulation is primarily established through an isolation housing whose inner wall is spaced from the pump head for the formation of a gas isolation layer. Through this effective insulation of the pump head, practically no heat can escape, so that it becomes particularly important to institute the measures pertaining to this invention for reducing the transmission of heat in the direction of the bearing of the connecting rod and crank mechanism.
The invention, along with its essential details, is described in more detail below.
In the drawings:
FIG. 1 is a longitudinal section of a measuring gas pump,
FIG. 2 is a partial cutaway of a connecting rod, and
FIG. 3 is a cross-section of a connecting rod in the area of a hole.